1. Field of the Invention
This invention relates to a process for recovering valuables from a waste etching solution containing a fluorine component and ammonia component and in particular, it is concerned with a process for recovering valuables from a waste etching solution containing a fluorine component and ammonia component, comprising recovering respectively a fluorine component and ammonia component in the waste solution and recovering a sodium component and/or potassium component used for processing the waste solution, and utilizing respectively the recovered components for preparation of a new etching solution or reusing or recycling for processing the waste solution.
2. Description of the Prior Art
As to waste etching solutions containing fluorine components and ammonia components discarded from the semiconductor and LSI industries, any effective processes for recovering valuables from the etching solutions have not been developed up to the present time, since it is considered hard to recover fluorine and ammonia as valuable components from the waste solutions.
As described above, any effective means for recovering valuable materials from an etching solution containing a fluorine component and ammonia component has not been developed, but an expedient processing means has been proposed.
The expedient processing means is generally carried out by a neutralization method with a low processing cost, in which slaked lime or cheap carbide sludge is used as a neutralizing agent.
In this neutralization method, only the fluorine component in the waste solution is fixed as CaF.sub.2 and subjected to abandonment, as a sludge with excess slaked lime, for reclamation. On the other hand, the ammonium component dissolved in the waste solution is diluted as it is and discharged. This ammonia component has been considered to nourish, as a nitrogen component, lakes, marshes and seas, and to cause red tide.
The amount of waste etching solutions containing fluorine components and ammonia components has been increased with the development of the semiconductor and LSI industries. Unless a technical development is made in the recovering process, therefore, it is supposed that serious problems arise such as increase of abandonment of sludges, discharge of nitrogen components, environmental pollutions, etc.
A technique for recovering valuable components from an etching solution containing a fluorine component and an ammonia component has also been proposed, but the recovered components are not used for resource-recycling. For example, Japanese Patent Publication No. 5366/1972 discloses a process for the production of ammonium hydrogen fluoride from ammonium fluoride, in which a low concentration aqueous solution of ammonium fluoride is heated at 50.degree. to 130.degree. C. under a pressure of at most 700 mmHg while maintaining a water content of 5 to 30 weight % and the thus generated steam and ammonia are removed, thereby obtaining an anhydrous crystal mixture of at least about 90 weight % of ammonium hydrogen fluoride and at most about 10 weight % of ammonium fluoride.
In this production process, the recovered valuable substance is the mixture of ammonium hydrogen fluoride and ammonium fluoride and has difficulty in handling, since in particular, ammonium fluoride is so thermally unstable that ammonia gas is released at a temperature of at least 40.degree. C. to form ammonium hydrogen fluoride and ammonium fluoride is more deliquescent than ammonium hydrogen fluoride.
Furthermore, this production process has the disadvantage that ammonia gas is generated with steam and due to the generation of ammonia gas, it is hard to treat the condensed water.
Japanese Patent Laid-Open Publication No. 265514/1991 discloses a process for processing a waste etching solution containing fluorine compound, comprising adding hydrofluoric acid and/or ammonia to the waste etching solution and forming an ammonium hydrogen fluoride solution, followed by recovering ammonium hydrogen fluoride as a crystal. However, this process has also a problem on effective recyling in a closed system.
As described above, any effective process for recovering valuables from an etching solution containing a fluorine component and ammonia component has not hitherto been developed and consequently, a serious problem on environmental pollution has been occurring with development of the semiconductor and LSI industries. Even if recovered, the recovered substance is only used as a component far from for resources-recycling.